Countess Margherita is a Sicilian girl who is about to be married, but Caesar Maruffi, the head of a criminal syndicate, wants her for himself. He arranges to have the bridegroom assassinated, and Norvin Blake, a young American (Robert Elliott), almost loses his life in his attempt to save him.

Richard Hall is a successful writer, while his wife, Alice, is interested in pursuing a career as a singer. She meets James Hamilton, a musical agent, who arranges an opera engagement with Rimini, an impresario. Hall quarrels with his wife over this, and they separate, with Hall taking their daughter Grace.

Sincere but struggling sculptor Tommasso (Caruso--bushy moustache, gawky) works in an ornamental plaster shop, but his masterpiece on the side is a bust of his cousin Caroli (Caruso--no moustache, polished), who is the Metropolitan Opera's leading tenor. Tommasso hopes to marry his model Rosa, but her father, restaurant owner Pietro, wants her to find someone more settled and money-conscious, such as the greengrocer Lombardi down the street. Tommasso, he says, throws away his money, such as for a pair of tickets to take Rosa to the opera to see his famed cousin. After the opera, the cousins cross paths in the swanky Galeotto's restaurant, but when neither recognizes the other, Tommasso is generally mocked and Rosa believes him a liar and unworthy. Tommasso must recover his reputation and make a sale, preferably the Caroli bust to his cousin, in order to win Rosa back.

Marcia Calhoun, a talented but penniless singer, leaves her Southern home hoping to study opera in New York. Her instructor, Professor Didot, promises her a contract on the condition that she receive formal training in Italy for one year. Didot introduces Marcia to millionaire Philip Bradley, who offers to pay for her studies if she will accompany him to Italy as his mistress. Desperate for money, she agrees, but several months later, Philip abandons her.

When composer Anselm Kardos leaves his alcoholic wife, he gives his daughter Lily an unfinished love ode entitled "The Song of Songs" and warns her to keep her artistic temperament in check.

In the days before the U.S. enters World War I Marion Ashley, an American woman living in Paris, discovers that her husband, Franz Jorn, is a spy. So she leaves him and goes to the neighboring (and fictional) neutral nation of Belmark to stay with her father, an American Ambassador. After she hears her husband has been killed, she resumes an old romance with the Crown Prince and they go through a secret morganatic marriage ceremony.

Story of the gentleman thief.

Natali, a Hindu, marries an Englishman, Sir Christopher Madgwick. They have a daughter who is kidnapped by Natali's former suitor Sani. The girl is handed over to be trained as a vestal virgin. Natali dies and Madgwick returns to England, taking with him the precious ruby that Natali had snatched from Sani in a struggle. Years pass; Sir Christopher remarries and has two more children who mistreat him and Sani dies, revealing to the priests the location of the ruby, which he stole from them in the first place.

Pierre Felix, a couturier, makes a $25,000 bet with Ralph Courtland that he can take a girl from the streets, dress her appropriately, and within three months have her accepted into society.

Although Raimond deMornay is in love with his cousin, Claire, his younger brother Louis wins her. Because of the intense jealousy he harbors towards Louis, Raimond goes to Vienna, and then to India. He returns home at the request of his nephew Paul -- Louis and Claire's son. But Raimond's jealousy is still overpowering, and with the aid of a box containing cobra poison, he murders his brother and hides his body in a casket.

Italian peasant girl deserts her fiancé for wealthy gangster and departs for America.

The wide-ranging storyline of The Melting Pot takes its characters from the Jewish ghettoes of Russia to the Lower East Side of New York.